# How can an UWB signal (pulse) radiate from an antenna?

This picture compares an uwb- and narrowband-signal: https://cdn.sewio.net/wp-content/uploads/2017/02/UWB-e1486395802254.jpg

Like I understand UWB, the signal("pulse") is directly put into the antenna. Using traditional modulation like AM, the amplitude/frequency pr phase of a sinusoidal signal would be changed according to the data signal. Such a signal then can easily radiate from an antenna (dipole) that is around half the wavelength of the carrier.

How can such an impulse "uwb-pulse" radiate from an uwb-antenna? There is no carrier that is modulated?

• Your understanding is incorrect. A narrow pulse is still baseband. It needs to be upconverted to the desired center frequency just like any other signal.
– MBaz
Mar 6, 2022 at 20:19
• To expand on my comment, here's a scenario. Consider a square pulse with duration 1 ns. Its bandwidth is, say, 3 GHz (2nd harmonic). Connected to an antenna with resonant frequency 1 GHz and BW of 500 MHZ, the pulse will generate energy in that band without needing a modulator. Is this what you have in mind?
– MBaz
Mar 6, 2022 at 20:26

Well, quite easily: A short impulse has a very wide spectrum, which means it contains large ranges of frequencies with significant power.

If you thus take a current impulse and put it to an antenna that can radiate a subset of these frequencies, it will radiate these.

This implicitly happens at every spark gap (the gap and supporting conductors forming kind of a badly-defined antenna). That's exactly what Heinrich Hertz used to prove the existence of electromagnetic waves, 1886.

In that sense, UWB produced through an impulse is the oldest intentional radio transmission.

here is no carrier that is modulated?

You could say that, but "modulating a carrier" is not the only way to get RF, as the pulse spectrum very well illustrates.

Same works directly and intentionally, too: If I take a 14 GS/s DAC (like the one in the arbitrary waveform generator at our university lab), and feed in pseudorandom numbers that were uncorrelated before I put them through a digital bandpass filter letting through 1 to 6 GHz, I get pretty much an UWB signal too. No explicit carrier involved.

UWB is still a radio technology; it still takes a pulse and modulates it by a carrier.

I'm not finding a definitive guide to the high:low frequency ratio, but if this Wikipedia table is anything to go by, it's in the range of 3:2, with an outlier at 2:1. That's well within wideband antenna technology (i.e. log-periodic antennas).

So the actual antenna part of the equation is quite solvable.